Typically, fuel cells are configured to generate electricity through an electrochemical reaction using a fuel gas and an oxidizing gas. The fuel cells have high power generation efficiency, and exhaust clean gases which can minimize negative effects on environments. Because of this, in recent years, it has been expected that the fuel cells are utilized for various uses such as power supplies for electric power generation and power supplies for automobile which provide less pollution. The fuel cells are categorized into plural kinds depending on the kinds of electrolytes which are components of the fuel cells. For example, there are known a phosphoric-acid fuel cell, a molten carbonate fuel cell, a solid oxide fuel cell, a polymer electrolyte fuel cell, etc. Among these fuel cells, the polymer electrolyte fuel cell can be operated at a low temperature of about 80 degrees C., and therefore is easily treated as compared to the fuel cells of another kinds. In addition, the polymer electrolyte fuel cell (PEFC) provides a very high output density. Under the circumstances, the utilization of the polymer electrolyte fuel cell is much expected.
Typically, the polymer electrolyte fuel cell includes a polymer electrolyte membrane having a proton conductivity, and a pair of electrodes which are an anode and a cathode provided such that they sandwich the polymer electrolyte membrane and face main surfaces of the polymer electrolyte membrane, respectively. In this way, the polymer electrolyte membrane and the pair of electrodes sandwiching the polymer electrolyte membrane constitute a membrane electrode assembly. A cell having a structure in which the membrane electrode assembly is sandwiched between separators is a minimum power generation unit. In the fuel cell, a fuel gas such as hydrogen or hydrocarbon is supplied to the anode, while an oxidizing gas such as oxygen or air is supplied to the cathode. Thus, an electrochemical reaction is caused to proceed in a three-phase interface among the gases, the electrolyte and the electrodes and electricity generated through the reaction is taken out.
As the polymer electrode membrane, an ion exchange resin having a skeleton which is mainly composed of a fluorine compound, or an ion exchange resin having a skeleton composed of hydrocarbon is used. These resins deteriorate with a long-period and continued operation of the fuel cell, and sulfur-based substance ions, fluoride ions, etc., are generated as substances resulting from decomposition. Among these substances, if the sulfur-based ions stay inside of the electrolyte membrane, the anode or the cathode of the fuel cell may be poisoned and an electrode effective area may be reduced. Specifically, the generated sulfur-based component is adsorbed onto a surface of a precious metal such as platinum constituting each electrode (to be precise, its catalyst) and as a result, the effective electrode area is reduced, which impedes the electrochemical reaction. Because of this, polarization of the cell increases and cell performance is degraded.
As a solution to this, there is a method for addressing degradation of the cell performance due to impurity ions. For example, Patent Literature 1 discloses a method in which water obtained by separating a gaseous component from an off-gas is caused to pass through an ion exchange resin to remove the impurity ions, and the resulting water is supplied to the anode, thus lowering an acid ion concentration in the water within the fuel cell and suppressing a corrosion of a metal member. Patent Literature 2 discloses a method of using a regenerant to regenerate an ion exchange resin having a degraded capability. Furthermore, Patent Literature 3 discloses a method in which a concentration of impurity ions contained in water generated during a power generation operation is measured, and a fuel cell is shut down and, for example, washed, when the measured concentration is high, thereby realizing a stable operation of a fuel cell for a long period of time.
Patent Literature 4 discloses a fuel cell power generation apparatus which humidifies a fuel cell using a humidified raw material gas at start-up. More specifically, the raw material gas humidified by a steam is supplied to the fuel cell through a reformer in a low temperature state. At a time point when the humidified raw material gas with a predetermined flow rate has been supplied, a temperature of the reformer is increased. Thus, a hydrogen-rich reformed gas derived by reforming the raw material gas is supplied to the fuel cell.